The present invention relates to the high throughput extrusion processing of advanced epoxy resins and coating compositions containing same.
Packaging coatings (e.g., for the interior of beverage cans and the like) previously have been formulated from advanced epoxy resins. For such purposes, it is desirable for the coating composition to have both good dry adhesion and wet adhesion properties.
Traditionally, batch processes have been used for the preparation of advanced epoxy resins. Unfortunately, however, these processes are expensive. They also unfortunately require the use of large amounts of solvent that poses manufacturing and potential environmental concerns.
Attempts have been made previously to process advanced epoxy resins using extruders. U.S. Pat. Nos. 4,612,156 and 5,310,854 describe two such attempts. Unfortunately, however, the methods disclosed in these patents have been found to yield inefficient throughput and, hence, are expensive to operate.
From the foregoing, it will be appreciated that what is needed in the art is a more efficient process that avoids the need for large amounts of solvent and that has high efficiency and throughput. Such methods for preparing advanced epoxies are disclosed and claimed herein.
In one embodiment, this invention relates to novel processes for preparing an advanced epoxy material. The process preferably comprises the steps of: continuously providing to an extruder: (i) an epoxy resin having an average of more than one vicinal epoxy group per molecule; (ii) a linking material having attached thereto an average of more than one moiety reactive with the vicinal epoxy group of the epoxy resin; and (iii) a catalytic amount of at least one iminium salt catalyst for promoting the reaction between the epoxy resin and the linking material; operating the extruder at a sufficient temperature (typically greater than 200xc2x0 C.) to cause a reaction between the epoxy resin and linking material for a sufficient residence time to produce an advanced epoxy resin; and continuously removing the produced advanced epoxy resin from the extruder.
In preferred embodiments the iminium salt catalyst has the general formula
R1R2R3P=N+=PR1R2R3 Zxe2x88x92
wherein each R1, R2 and R3 is independently an aromatic, inertly substituted aromatic, aliphatic, cycloaliphatic, inertly substituted aliphatic, or inertly substituted cycloaliphatic group; and Z is any suitable anion. In most preferred embodiments the catalyst is a bis(triphenylphosphine) iminium salt.
As used herein, the term xe2x80x9chydrocarbylxe2x80x9d means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic or cycloaliphatic, or aliphatic or cycloaliphatic substituted aromatic groups. The aliphatic groups can be saturated or unsaturated.
As used herein, the term xe2x80x9chydrocarbyloxyxe2x80x9d means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
As used herein, the xe2x80x9creaction timexe2x80x9d for an extruder process equals the average residence time a unit mass of material at steady state spends in the reaction section of the extruder.